Diesel engines compress air-fuel mixtures to initiate combustion in engine cylinders. Glow plugs may be used during starting of a cold diesel to assist engine starting when compression of the air-fuel mixture may be insufficient to produce automatic ignition of an air-fuel mixture. The glow plugs may be positioned in a combustion chamber to elevate the temperature of a portion of an in cylinder air-fuel mixture so that the air-fuel mixture may ignite when compressed. Once the engine is started the glow plugs are turned off to conserve energy and extend glow plug life. However, it may not be desirable to deactivate glow plugs after an engine start simply because the engine is started. Further, it may be desirable during some engine operating conditions to control glow plugs responsive to conditions other than an indication that an engine is started.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine operating method, comprising: performing combustion in a cylinder of an engine; and increasing a negative torque output of a motor to the engine in response to anticipated activation of the glow plug.
By selectively increasing a negative torque of a motor coupled to an engine, it may be possible to delay entering low engine load conditions where combustion stability may be less than is desirable before glow plug reaches a desired operating temperature. For example, a glow plug may require several to tens of seconds to reach a desired operating temperature where the glow plug can improve combustion stability in the cylinder at low engine loads. If the engine where to enter low load conditions before the glow plug reaches the desired operating temperature, engine combustion stability may degrade. However, engine load may be increased while a desired net driveline torque is output to vehicle wheels by increasing negative torque of a motor coupled to the engine. In this way, the engine may be operated at conditions where combustion stability is at a desired level while the glow plug temperature increases.
The present description may provide several advantages. In particular, the approach may improve engine operation during low load conditions. In addition, the approach provides compensation for glow plug heating response time. Further, the approach may reduce engine emissions after the engine reaches warmed up operating conditions by allowing the engine to retard combustion phasing while continuing to provide stable combustion.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.